The present invention relates to the manufacture of hollow tubular elements. More particularly it relates to a novel apparatus adapted for manufacturing hollow tubular elements of the type formed from a spiral-wound strip.
The manufacture of hollow tubular elements from a strip of materials from a great variety of sources, spirally wound continuously until reaching a particular length, has long been known. The process for the manufacture of this type of tubular elements, however, had always been of the intermittent or non-continuous type, that is, a process wherein the manufacture of a length of tubular element of predetermined length was performed on an apparatus suitable for the purpose. After the stages of the manufacturing process were completed, the tubular element thus formed had to be withdrawn from the apparatus, and the said apparatus had to be prepared for the production of another length of similar characteristics, totally independent of the first, and so on.
U.S. Pat. No. 3,809,514, granted to Julio de Castro Nunez, entitled, "MACHINE FOR THE CONTINUOUS MANUFACTURE OF HOLLOW ELEMENTS," describes and claims an apparatus for manufacturing said tubular elements continuously. In the method of using the said apparatus, the spiral winding of the continuous strip forming the hollow element is performed continuously in the apparatus, automatically, as the spirals of the tubular element are made to advance towards the output end of the apparatus, where the formed tubular element is continuously delivered in a self-supporting condition, in a single strand of indefinite and continuous length. That is to say, by means of the apparatus of the said De Castro patent, a hollow tubular element can be obtained of appropriate size and of indefinite length.
The inventive principle of the patent mentioned above is based essentially on the use of an apparatus of elongated, generally cylindrical configuration, formed by a plurality of elongated, mold-forming elements on which there is disposed a continuous band supported on the said devices, and helically wound such that the spirals of the winding do not overlap one another nor separate substantially, but extend side by side. At the output end of the apparatus, the said continuous band is returned towards the starting or input end along an axial path through the center of the winding. The entire assembly thus disposed receives a rotational movement on the axial shaft of the cylinder, such that the said movement will continuously produce the advancement of the spirals towards the output end, from which the continuous band is continuously returned, as stated above. The elongated, mold-forming elements do not follow a straight path along the axial plane of the assembly, but are oriented with a slight tilt so as to favor the movement of the continuous band in the manner mentioned above.
Although this apparatus works, and is capable of producing the effects that it is said to produce (that is, a continuous tubular element from a continuous strip of material wound spirally with a partial overlap), it has a number of disadvantages and difficulties with the result that its employment has not been as widespread as an improvement of such nature over the prior art might have been expected to have.
Indeed, among the chief difficulties from which this apparatus suffers is the fact that the continuous band must be made of a highly flexible material so as to permit the abrupt bend at the output end for its return to the input end. This implies that the band must have a small thickness so as to be able to adapt perfectly to the circumference of the mold, and can accomplish the return perfectly. But, since the continuous strip from which the tubular element is to be formed, upon being wound upon the said continuous band, places tensile stress on the band along the entire length of the wound surface, the loss of the arrangement of the turns one beside the other is frequent, and therefore one or more of the said spirals pile up or overlap, resulting in the intensifying of the tensile stresses on the spiral that remains underneath, and this occasionally results in the breaking or bursting of the said continuous band at that point. Needless to say, when this event occurs, and it is quite frequent, it is necessary to stop the process, remove a substantial portion of the formed but unfinished tubular element, with a loss of time and materials and repair costs.
Other times the phenomenon mentioned above produces the result that the contiguous spirals of the continuous band separate too much from one another, thus permitting the fluid or semi-fluid material being used to pass from the molding surface defined by the spirals to the inside thereof, that is, on the mold-forming elements. Since these elements must be animated with movement, there is a plurality of wheels on which they are seated, which, when they remain in reach of the fluid or semi-fluid material, ordinarily a resin, will fail to operate properly, or will not operate at all, depending on the degree of resin clogging, and on the physical characteristics of the resin. When this is the case, it will also be necessary to halt the process, remove the continuous band, take apart the roller assembly and wheels and clean them individually so as to eliminate the resin, with the concomitant loss of time, labor, materials, etc.
Another very important disadvantage in the apparatus in question is the fact that the roller elements or the like, mentioned above, are not disposed continuously over the entire length of the apparatus, but are distributed more or less equidistantly therein, with intermediate portions of substantial length. Since the winding tensions of the continuous band are high, as stated previously, and since these tensions are increased by those produced by the continuous strip of material from which the continuous tubular element is formed, it is obvious that, in those intermediate portions lacking direct support from the wheels or the like, said tensions will produce flexing in the mold forming elements, whereby the cross section of the said mold will be altered, thus producing a tubular element of irregular section which is commercially unacceptable. In addition, this alteration of the level of the mold forming elements is also liable to produce overlapping of the continuous band, resulting in occasional breakage, as well as the formation of gaps between spirals in the contrary case, so that the fluid materials indicated before will enter in.
Another important disadvantage of the above-mentioned apparatus is based on the fact that the helical arrangement of the continuous band defines between two contiguous spirals, tending to produce a rib or helical protuberance on the inside of the formed tubular element, which will constitute a defect from the product quality viewpoint, since this rib will tend to produce turbulence in the liquid that is being carried inside of the tubular element when in use.
As a corollary of all the disadvantages cited above, it is to be stated that, due to the oblique or diagonal arrangement of the roller elements or the like, their correct arrangement is a tedious and slow job, inasmuch as a slight difference in the arrangement of one of these elements can create localized stresses which also will tend to overlap the spirals or the continuous band or break the latter. Therefore, every time that one of the circumstances mentioned above makes it necessary to disassemble the roller and wheel elements, a carefully controlled reinstallation of them must be performed, which makes the job of resumption of activities a very serious problem.
As it will be understood from what is set forth above, the frequent interruption of the operation of the apparatus of U.S. Pat. No. 3,809,514 very greatly reduces its output in terms of units of length of the tubular element in the time of operation of the apparatus, the quality of the element obtained does not satisfy the requirements of the market in many ways, and the workers needed for tending the apparatus must be highly skilled, all of which results in low profitability of the apparatus. Therefore, an apparatus for the continuous manufacture of hollow tubular elements is needed which will not have the disadvantages of the apparatus of the above-cited U.S. patent.